Altered ventral neck muscle deformation for

individuals with whiplash associated disorder

compared to healthy controls - A case-control

ultrasound study

Gunnel Peterson, Asa Dedering, Erika Andersson, David Nilsson, Johan Trygg, Michael

Peolsson, Thorne Wallman and Anneli Peolsson

Linköping University Post Print

N.B.: When citing this work, cite the original article.

Original Publication:

Gunnel Peterson, Asa Dedering, Erika Andersson, David Nilsson, Johan Trygg, Michael

Peolsson, Thorne Wallman and Anneli Peolsson, Altered ventral neck muscle deformation for

individuals with whiplash associated disorder compared to healthy controls - A case-control

ultrasound study, 2015, Manual Therapy, (20), 2, 319-327.

http://dx.doi.org/10.1016/j.math.2014.10.006

Copyright: Elsevier

http://www.elsevier.com/

Postprint available at: Linköping University Electronic Press

http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-115920

Altered ventral neck muscle deformation for individuals with Whiplash

Associated Disorder compared to Healthy Controls; a case-control Ultrasound

study

Gunnel Peterson, PT, MSc,1,2, Åsa Dedering,PT PhD3, Erika Andersson, MSc2, David Nilsson

Phd4, Johan Trygg PhD, Prof4, Michael Peolsson CE, Phd4, Thorne Wallman, MD, PhD1, 5,

Anneli Peolsson, PT, PhD, Assoc. Prof2

1 Centre for Clinical Research Sörmland, Uppsala University, Eskilstuna, Sweden

2Department of Medical and Health Sciences, Division of Physiotherapy, Faculty of Health

Sciences, Linköping University, Linköping, Sweden

3Department of Neurobiology, Care Sciences and Society, Division of

Physiotherapy, Karolinska Institutet and Department of Physical Therapy, Karolinska

University Hospital, Sweden

4 Department of Chemistry, Computational Life Science Cluster, Umeå University, Sweden

5Uppsala University, Public Health & Caring Sciences, Family Medicine & Preventive

Medicine Section, Uppsala, Sweden

Address correspondence to Gunnel Peterson, Division of Physiotherapy, Department of

Medical and Health Sciences, Linköpings University, SE-581 83 Sweden. E-mail:

gunnel.peterson@liu.se

Keywords

Whiplash injury; ultrasonography; neck muscles

INTRODUCTION

Some long-lasting symptoms associated with whiplash-associated disorders (WAD)

(Berglund et al., 2001; Kongsted et al., 2007; Carroll et al., 2009) may be due to impaired

neck muscle function with altered motor control patterns (Jull et al., 2004; Woodhouse and

Vasseljen, 2008; O'Leary et al., 2011). Changed activation of the deep muscle layer (Falla et

al., 2004a), which is thought to stabilize the spine (Panjabi, 1992; Mayoux-Benhamou et al.,

1994), might increase neck disability. Magnetic resonance imaging can non-invasively

distinguish between the deep cervical flexors, longus capitis (Lcap), and longus colli (Lco)

(Cagnie et al., 2008; Cagnie et al., 2010; Elliott et al., 2010); but cannot be used to investigate

muscles during movement. Surface electromyography (EMG) has demonstrated increased

activity in the sternocleidomastoid (SCM) muscle (Falla et al., 2004b; Jull et al., 2004) and

invasive EMG studies (electrode contacts inserted through the nose) reported a delayed

activation of the deep cervical flexors in chronic neck pain (Falla et al. 2004a; Falla et al.

2004c). Nevertheless, EMG investigations run a risk of cross-talk between muscles, and

cannot distinguish between the Lcap and Lco. Still image ultrasonography can measure the

thickness of deep ventral neck muscles (Cagnie et al., 2009; Javanshir et al., 2011), but it

provides no information about neck muscle function during real-time motion. With

ultrasound, the muscle of interest may be influenced by neighboring tissues or external

pressure from the probe. Nevertheless; the ability to investigate deep and superficial muscle

functions together, during real time activations (Lopata et al., 2010; Peolsson et al., 2010

Peolsson et al., 2014) makes this method interesting. Speckle tracking is a post-process

method for analyzing ultrasound images; it facilitates measuring muscle deformations

(elongations and shortenings) and deformation rates, and this information has improved our

understanding of real time (Lopata et al., 2010) mechanical neck muscle function in different

muscle layers (Peolsson et al., 2012). To our knowledge, this approach has not been

previously applied in individuals with chronic WAD. The objective of the present study was

to compare deformations and deformation rates in the SCM, Lcap, and Lco in individuals

with WAD vs. control subjects, during repetitive arm elevations. In addition, we aimed to

determine if the interplay of the three muscles differed between the WAD and control groups.

We hypothesized that deformation and deformation rates would be increased in the SCM and

decreased in the Lcap and Lco for individuals with chronic WAD compared to healthy

controls.

METHODS

Participants

Twenty-six individuals, 20 women and 6 men (mean age 37 years, SD; 10.6) with persistent

neck pain after a whiplash injury and 26 controls, matched for age and sex, participated in the

study (Table 1). As no previous study has compared deformation and deformation rate

between WAD and controls, the sample size was arbitrary.

Individuals with WAD were consecutively recruited for ultrasound investigation from a

larger, ongoing, randomized controlled trial (Peolsson et al., 2013).

For study eligibility, individuals had to report neck pain in the right side of the neck, right-

handedness, and fluency in Swedish. Study inclusion criteria were positive manual

examination findings that corresponded to WAD grade II (neck pain and musculoskeletal

signs) or III (neck pain plus neurological signs) (Spitzer et al., 1995); persistent neck pain

rated greater than 20 mm on a visual analogue scale (VAS), and/or neck disability greater

than 20% (MacDermid et al., 2009), measured with the neck disability index (NDI); aged 18

– 63 years; and ongoing symptoms associated with a whiplash injury that started six months

to three years prior to study entry.

Exclusion criteria were signs of traumatic brain injury at the time of whiplash injury; known

or suspected serious pathology; previous fracture or luxation in the cervical spine;

contraindication to exercise; neuromuscular diseases; rheumatologic disease; previous serious

neck pain that warranted more than 1 month of sick leave in the year prior to their whiplash

injury; severe mental illness; or current alcohol or drug abuse.

The healthy controls were recruited from university staff, hospital staff, and acquaintances.

Exclusion criteria were current or past neck problems; trauma to the neck or head including

whiplash injury; neck or low back pain; rheumatologic or neurologic disease; or generalized

myalgia. The study was approved by the Regional Ethics Review Board and was conducted

according to the Declaration of Helsinki. Written informed consent was obtained from all

participants.

Ultrasound measurements

The ventral neck muscles were recorded with a B-mode, 2-D ultrasound Vivid-I scanner (GE

Healthcare, Horten, Norway). The ultrasound was equipped with a 12 MHz linear transducer

(38 mm) with high frame rate (235 frames/s). Ultrasound measurements of the SCM, Lcap,

and Lco were recorded during repetitive arm elevations. Each test included 10 arm

elevations, and ultrasound images (“video” sequences) were acquired during the first and

tenth arm elevations. The ultrasound probe was positioned at the C4 level on the right side of

the neck (Fig. 1a). The segmental level was verified with a transverse ultrasound projection

of the bifurcation of the carotid artery, commonly observed at the C4 level. The transducer

was then rotated to a longitudinal position, which allowed optimal imaging of the SCM,

Lcap, and Lco muscles. All ultrasound measurements were acquired in this longitudinal

position (Fig. 1b).

Speckle tracking

Ultrasound of muscle results in reflection of sound waves, which serve as acoustic markers

because they form a unique speckle pattern. Briefly, a region of interest (ROI) was manually

placed in the first frame of the video sequence of each muscle. Tracking the unique speckle

pattern of the respective ROI was based on an algorithm developed by Kanade-Lukas-Tomasi

(KLT) (Lucas and Kanade, 1981; Tomasi and Kanade, 1991), which was further enhanced

(Farron et al., 2009). Accordingly, when the muscle speckle pattern changes length, the

tracked ROI also changes in length, and the unique pattern can be followed frame by frame

throughout the ultrasound images. The ROI comprises a large number of points placed

equidistant between the two endpoints. The frame to frame displacement can then obtained

with a least squares fit, assuming a linear strain model. The displacement of all points within

the ROI were summed, to obtain a cumulative sum from all frames in the movie which

provided quantitative information of muscle behavior during the arm elevation.

Muscle Deformation was defined as a change in ROI length (elongation or shortening),

calculated as the percentage change (% deformation) from the original length; provided

information about local tissue dynamics. The Muscle Deformation Rate was defined as the

rate of the change in deformation, expressed as the amount of deformation per time unit (%

deformation/s). Three ROIs (each ROI was 10 × 3.3 mm) were positioned longitudinally in

each of the muscles (i.e., oriented longitudinal to the muscle fibers); together, the three ROIs

covered 30 mm of the unique speckle pattern in each muscle (Fig. 2). The magnitude of

muscle deformation measured with speckle tracking was positively related to other

measurements used to investigate muscle deformation (force measurements and progressive

electrical stimulation) (Lopata et al., 2010). The reliability of the speckle tracking analysis

method was shown to have excellent test-retest reliability (two-way random absolute

agreement single measure intraclass correlation coefficient [ICC)] 0.71-0.97) (Peolsson et al.

in press).

Test procedure

Two experienced physiotherapists were present during the test, one performed the ultrasound

examination and the other assisted the ultrasound examiner. The experiment was designed to

resemble activities that might increase neck pain in individuals with poor functional recovery

after whiplash injury; for example, performing a job with repetitive arm lifting (Sullivan et

al., 2010). To standardize the test; we included only right-handed individuals with dominant

right-sided neck pain (Fig. 1b). Before the measurements began, the individual practiced the

test with the left arm.

Other measurements

Pain

The average pain intensity experienced over the prior week was assessed with a visual

analogue scale (VAS 0-100 mm scale, 0 = no pain, 100 = worst imaginable pain) (Carlsson,

1983).

Neck disability

Disability was measured with the neck disability index (NDI). The NDI consists of 10 items,

expressed as a percentage (total possible score 100%), with higher scores indicating greater

disability (MacDermid et al., 2009).

Physical activity

Subjects answered questions about daily life activities (walking, cycling to work etc.) and

exercise beyond daily life activities performed over the last 12 months. The answers were

combined to calculate the activity index (1 = inactivity, 2 = low activity, 3 = moderate

activity, 4 = high activity) (Kallings et al., 2008).

Neck muscle fatigue

The participants rated fatigue in the neck muscles before and after the ultrasound test on a

Borg CR-10 scale (0 = no fatigue, 10 = extremely strong fatigue), (Borg, 1990).

Data analyses

Ultrasonography data were post-processed with speckle tracking methodology implemented

with a program designed in-house for Matlab (Matlab., 2013). The KLT tracking algorithm

was part of the Computer Vision toolbox of Matlab. To evaluate muscle deformations for the

first and tenth arm elevations, the areas on the deformation curves were calculated (Fig. 3).

Deformation rate results are presented as the root mean square (RMS), which gives

information about the local tissue velocity of deformation. Therefore, the deformation and

deformation rate measure the mechanical function of the muscle.

The ultrasound video images were coded during the post-process analyses. Thus, the analyzer

(the PT with three years of experience with speckle-tracking analyses) was blinded to the

group affiliation

Statistical analyses

All data analyses were performed with SPSS statistical software, version 20. Demographic

variables were compared between groups using the two-tailed unpaired Students t-test and the

Chi2 test. Between-group differences in physical activity levels and neck muscle fatigue were

analyzed with the Mann Whitney U test.

Deformation measurements were skewed; therefore, non-parametric tests were applied. The

deformation rate data were normally distributed and parametric tests were applied. The

correlations of deformations among the SCM, Lcap, and Lco during the first and tenth arm

elevations were evaluated with Spearman’s rho test (for deformation) and Pearson’s

correlation (for deformation rate). Linear regression models were applied to investigate the

relationships of the deformations and the deformation rate among the three muscles

(SCM/Lcap, SCM/Lco, Lcap/Lco) for individuals in both groups (control and WAD). One

outlier (WAD) in the deformation rate and one outlier from each group (WAD/Control) in the

deformation had some impact on the results for correlation and linear regression analysis;

therefore these where excluded from the analysis.

A mixed design analysis of variance (ANOVA) with Bonferroni correction was used to

evaluate the change in deformation rate. The groups (control and WAD) were the between-

subjects variable, the three muscles (SCM, Lcap, and Lco) were the within-subject variables,

and the analysis was adjusted for the duration of each arm elevation. The deformation values

were positive-skewed, and the assumptions of variance were violated (Levene´s test p <

0.05). Thus, the data were analyzed with the non-parametric test, Friedman ANOVA, and the

Mann Whitney U test.

We used the Wilcoxon signed-rank test for paired two group analyses of differences in the

deformation between the first and tenth arm elevations and the paired sampled T-test for

deformation rates. P-values ≤0.05 were considered significant. Effect sizes (ES) were

calculated for the deformations 𝐸𝑆 =𝑍

√𝑁 (non-parametric; z-score divided by the square root

of the number of total observations [N]) and deformation rates 𝐸𝑆 = √𝑡2

𝑡2+𝑑𝑓 (parametric; the

square root of the t-score x t-score (t2) divided by t2 + degree of freedom [df])

RESULTS

Deformation

Comparisons between the WAD and control groups

When evaluating deformation, the only significantly different finding was that the SCM was

less elongated in individuals with WAD compared with controls during the first arm

elevation (Table 2).

Comparison between the first and tenth arm elevations

In controls, all three ventral neck muscles showed significantly less deformation (total area)

during the tenth arm elevation compared to the first elevation and the muscles were activated

with less shortening (ES: 0.42 to 0.70). In individuals with WAD, only the SCM showed less

deformation in the tenth than in the first elevation, and it was also activated with less

shortening (ES: 0.68) (Table 2).

Deformations of SCM, Lcap, and Lco during the first and tenth arm elevations

In both groups, the deformations observed in the three muscles were significantly different

during the arm elevations. The total area was lower in the SCM than the Lcap and Lco.

Correlation

When control subjects performed arm elevations, the deformations in the first elevation

significantly correlated between SCM/Lcap (r = 0.50) and SCM/Lco (r = 0.59); in addition,

the strength of correlations increased during the tenth arm elevation for all three muscle pairs

(r = 0.51 to 0.80). For individuals with WAD, there was no correlation among muscles during

the first arm elevation, while there were correlation between SCM/Lcap (r = 0.40) and

Lcap/Lco (r = 0.73) during the tenth elevation during the tenth elevation (Table 3).

Linear relationship

For controls, there was a positive linear relationship between all muscle pairs (SCM/Lco,

SCM/Lcap, and Lcap/Lco ) that increased from the first to the tenth arm elevation. In

contrast, individuals with WAD, only showed a positive linear relationship for Lcap/Lco

during the tenth arm elevation (Fig. 4 a-f).

Deformation rate

Differences in deformation rates between and within groups (control and WAD)

A significant main effect between groups was observed in the deformation rate during the

tenth arm elevation, F(1,48) = 5.3 (p < 0.01), where individuals with WAD showed an

increased Lco deformation rate compared to controls F (1,48) = 4.6. In addition, both groups

showed a significant interaction effect between muscles, the SCM showed a lower rate than

Lcap and Lco in the tenth arm elevations, F(1,48) = 7.2 (p < 0.01). No significant between-

group effect was observed during the first arm elevation, F(1,46) = 0.81. For controls, the

deformation rates decreased during the tenth arm elevation compared to first in all three

muscles. For individuals with WAD, the deformation rates only decreased in the tenth arm

elevation compared with the first for the SCM (Table 4).

Correlation

For controls, during both the first and tenth arm elevations, the deformation rates were

significantly correlated among all three muscles (r = 0.51 to 0.84). For individuals with

WAD, the first arm elevations, showed significant correlations among all three muscles (r =

0.55 to 0.66); while, in the tenth arm elevations only the Lcap and Lco were correlated (r =

0.49) (Table 3).

Linear relationship

For controls, the positive linear relationship for SCM/Lcap increased from the first to tenth

arm elevations. The relationships between SCM/Lco and Lcap/Lco were the same for both

arm elevations. Individuals with WAD, showed a decreased linear relationship from the first

to tenth arm elevations for all three muscle pairs (Fig 5 a-f).

Neck muscle fatigue

The WAD group showed significantly higher fatigue (median 4.0, IQR: 2.7 to 5.2) compared

to controls (median 0.0, IQR: 0 to 0) (p < 0.001) before the first arm elevation. After the tenth

arm elevation the fatigue did not changed for either group (WAD [median 4.0, IQR: 2.7 to

6.0], controls [median 0.0, IQR: 0 to 0.1]).

DISCUSSION

We found only a few significant differences between individuals with WAD and healthy

controls in the deformations and deformation rates for the SCM, Lcap, and Lco muscles. Our

results did reveal that the interplay between pairs of muscles, SCM/Lco, SCM/Lcap, and

Lcap/Lco, was altered in the WAD group compared with the control group. Based on earlier

studies, we hypothesized that SCM activity would increase and activity in the deep neck

flexors would decrease during arm movements for individuals with WAD compared to

controls (Falla et al., 2004b; Falla et al., 2004c; Jull et al., 2004). However, our results did not

confirm the hypothesis of group differences between healthy controls and individuals with

WAD. An explanation could be that highly individual muscle patterns, made it difficult to

detect significant differences between groups, due to large standard deviations. Another

explanation for the lack of differences in group level findings could be that ultrasound data

from the present study were not directly comparable to EMG data from earlier studies (Falla

et al., 2004a; Falla et al., 2004b; Jull et al., 2004). EMGs measure muscle action potentials,

which reflect the chemical-electrical changes in muscles and nerves; in contrast, real-time

ultrasound measure deformation. Deformation was calculated from a series of measurements

(235 measurments/s) taken during arm elevation (average elevation time 2.5 s), that produced

a curve of muscle elongation and shortening (Fig. 3). On that curve, a greater area

represented greater deformation.

In controls, we observed an individual muscle pattern of low deformation and deformation

rates or high deformation and deformation rates in SCM/Lco, SCM/Lcap and Lcap/Lco. In

individuals with WAD, this correlation was altered, which may indicate diminished

cooperation between muscles after ten arm elevations. The linear relationship between

superficial and deep neck muscles (SCM/Lco and SCM/ Lcap) was increased in the control

group (moderate to strong) compared to the diminished or weakened relationship for the

WAD group (Fig 4 and 5 a-d). The linear relationship between Lcap/Lco deformations

increased from weak to moderate from the first to tenth arm elevation in both the WAD and

control groups (Fig 4 e,f). However, the relationship between the Lcap/Lco deformation rates

decreased from moderate to weak from the first to tenth arm elevation in the WAD group;

whereas, controls showed a moderate relationship during both the first and tenth arm

elevation (Fig 5 e,f). Thus, although the groups showed similar relationships in deformation

in Lcap/Lco, the relationship between the deep muscle deformation rates weakened with time

for the WAD group. In light of this finding and reports from other studies (Hodges et al.,

2013; Hug et al., 2013), it appears that comparing the individual relationships among muscles

is informative. In addition, ultrasound speckle tracking can be a complementary analysis to

neck muscle activations detected by EMG (Falla et al., 2004a).

The WAD group reported fatigue even before the first arm elevation, and the relationships

between several muscles had weakened after ten arm elevations. The deformation rate

included both acceleration and deceleration rates (RMS). Thus, both high deformation rates

and no correlations between muscles (e.g., when a car accelerates or brakes all the time) may

indicate an ineffective muscle activation pattern that could result from or cause fatigue and/or

pain.

Limitations and further recommendations

Ultrasound with post-process speckle tracking provides a non-invasive method to investigate

muscle deformation in real time (Lopata et al., 2010; Peolsson et al., 2012). However,

although the method was sucessfully validated against force measurements (Lopata et al.,

2010), more studies are required to validate this method. The probe pressure and possible

small neck movements during the test could have influenced the results. Also, the lack of

significant anatomical landmarks could have limited the precision of probe placement;

however, the bifurcation of the carotid artery (commonly at the C4 level) (Civielek et al.

2007) and the vertebral column were used as reference points. Another potential limitation of

the study was that the ROI was selected manually for each muscle of interest. Thus, like in

EMG investigations, the ROI may not adequately represent the whole muscle. Real time

ultrasound investigation causes some uncertainty if the probe is placed in the same area in all

study participants. However, we studied three ROIs that covered 30 mm of the muscle (probe

size 38 mm); this larger area would minimize the differences between inidviduals and

increase measurment accuracy. In the WAD group, eight (of 26) participants had neurological

symptoms (grade III); which could have affected the results, due to potential changes in

dorsal nerves and neck muscle interactions.

CONCLUSION

This study showed only a few group differences in the deformations and the deformation

rates in the SCM, Lcap, and Lco muscles when comparing individuals with WAD and

healthy controls. This study demonstrated that, in the control group, the deformations and

deformation rates in one muscle correlated with deformations and deformation rates in other

neck muscles. This interplay between muscles was altered in individuals with WAD. Further

studies are required to develop a mathematical model that can determine when the neck

muscle activation pattern becomes abnormal.

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Table 1. Characteristics of participants in the study

WAD (N=26)

Healthy controls

(N=26)

P

Gender, female (number and %) 20 (77%) 20 (77%) 1.0

WAD grade II/III (number) 18/8 0 0.001

Age (years; mean and SD) 37 (10.9) 37(10.9) 0.96

Injury durationa (months, mean and SD) 22 (7.7) 0 < 0.001

BMI b male (mean and SD) 25 (6.6) 25 (3.5) 0.81

BMI female (mean and SD) 25 (5.4) 22 (2.4) 0.01

Physical activity levelc (median and range) 2 (2 - 3) 4 (3 - 4) 0.001

Neck Disability Index d (mean and SD) 34 (13.4) 1 (1.6) 0.001

Pain previous week e (VAS; mean and SD) 50 (18.8) 1 (1.0) 0.001

a) Months since whiplash injury, range 6 to 36 months.

b) BMI; Body Mass Index (kg/m2).

c) Physical activity level over the prior 12 months (1 = inactivity, 2 = low activity, 3 =

moderate activity, 4 = high activity)

d) Neck Disability Index Score (0-100%) was based on 10 items; higher scores

represented higher disability.

e) VAS; Visual analogue scale, average pain in the prior week, range 0-100 mm, higher

rating represented higher pain intensity.

Table 2. Muscle deformations (% change in length) during the first (1st) and the tenth (10th) arm elevation. Total area represents the sum of

elongations and shortenings of the muscle, expressed as the median and interquartile range (IQR) for each group.

Control (n = 25) WAD (n= 25) Between groups Effect size Effect size

p-value p-value between groups 1st to 10tha

1st 10th 1st 10th 1st 10th 1st 10th Control WAD

Test timeb 2.38 (0.34) 2.38 (0.35) 2.50 (0.39) 2.42 (0.44) 0.18 0.72

Total area SCM 5.8 (4.5 – 11.5) 3.6 (2.1 – 5.9)* 5.2 (3.7 – 8.6) 3.5 (3.0 – 4.6)* 0.24 0.91 0.16 0.13 0.70 0.68

Lcap 10.8 (7.5 – 13.7) 6.7 (4.9 – 9.1)* 10.1 (7.1 – 12.6) 7.8 (5.3 – 13.0) 0.33 0.38 0.14 0.04 0.70 0.32

Lco 10.8 (7.5 – 13.3) 7.1 (4.8 – 11.7)* 9.3 (6.2 – 13.8) 7.9 (6.0 – 15.7) 0.56 0.26 0.08 0.16 0.42 0.11

Elongation SCM 2.6 (1.7 – 3.9) 1.2 (0.7– 2.7)* 1.4 (0.5– 3.3) 1.5 (1.1 – 2.8) 0.02 0.72 0.34 0.07 0.62 0.09

Lcap 4.2 (2.1 – 7.7) 2.8 (1.6 – 3.9) 4.0 (2.3 – 6.2) 2.8 (1.5 – 5.2) 0.83 0.38 0.03 0.05 0.28 0.39

Lco 2.9 (1.7 – 4.4) 3.0 (1.7 – 4.8) 2.3 (1.1 – 5.0) 3.2 (2.2 – 6.3) 0.55 0.55 0.09 0.08 0.08 0.44

Shortening SCM 3.3 (1.7 – 8.1) 1.4 (0.8– 3.0)* 3.6 (1.6 – 5.9) 1.9 (0.9 – 3.2)* 0.82 0.74 0.03 0.13 0.65 0.68

Lcap 6.3 (3.2 – 8.3) 4.2 (2.8 – 6.2)* 6.1 (2.6 – 7.9) 4.9 (2.4 – 7.2) 0.74 0.69 0.05 0.08 0.42 0.08

Lco 6.2 (5.0 – 11.0) 4.2 (2.6 – 7.7)* 6.4 (3.9 – 10.8) 4.7 (2.1 – 10.4) 0.85 0.66 0.12 0.06 0.55 0.35

a Effect size for the within group changes from the 1st to 10th arm elevation.

b Test time in seconds for the 1st and 10th arm elevation, mean (SD).

*Significant differences (p < 0.05) between the first and tenth arm elevations

Table 3. Correlations between the sternocleidomastoid (SCM), longus capitis (Lcap), and longus colli (Lco) muscles in deformations and

deformation rates during the first (1st) and tenth (10th) arm elevations for individuals with WAD and healthy controls.

Deformation

1st

Deformation

10th

Deformation rate

1st

Deformation rate

10th

Lcap Lco Lcap Lco Lcap Lco Lcap Lco

Control SCM .592** .502* .731** .802** .515* .780** .841** .836**

Lcap .371 .776** .575** .725**

WAD SCM .165 -.049 .398* .110 .658** .550** .347 .380

Lcap .356 .730** .654** .495*

*p<0.05, **p<0.01

Table 4.

Deformation rate (% deformation/s) in sternocleidomastoid (SCM), longus capitis (Lcap) and longus colli (Lco) during the first (1st) and tenth

(10th) arm elevations, mean (SD).

Control WAD Between groups Effect size Effect size

p-value p-value Between groups 1st to 10tha

1st 10th 1st 10th 1st 10th 1st 10th Control WAD

SCM 0.19 (0.07) 0.13 (0.04)* 0.19 (0.07) 0.15 (0.04)* 0.82 0.28 0.03 0.15 0.88 0.66

Lcap 0.28 (0.07) 0.22 (0.05)* 0.29 (0.08) 0.26 (0.07) 0.68 0.08 0.06 0.25 0.65 0.35

Lco 0.30 (0.08) 0.24 (0.07)* 0.33 (0.10) 0.29 (0.09) 0.22 0.03 0.18 0.31 0.62 0.30

a Effect size for the with-in group changes from the 1st to 10th arm elevation.

*Significant differences (p < 0.05) between first and tenth arm elevations

Fig. 1a. Position of the ultrasound probe.

Fig. 1b. Ultrasound imaging of ventral neck muscles during arm elevation. The arm was

raised to 90 degrees, and an adjustable horizontal bar was fixed with the index finger

touching the bar. The subject held a weight of 0.5 kg (women) or 1 kg (men) in the right

hand. A pair of customized contact switches was attached to the subject, one on the right

wrist and one on the right hip. The contact signal was recorded in the ultrasound machine in

the channel for the EKG system, to provide a cue for synchronizing data between the

ultrasonograph and the starts and stops of arm movements.. A metronome was set at 40 beats

per minute to maintain a steady pace during the examination. Each individual was asked to

stand in an upright, comfortable position, with feet behind a line marked on the floor. The

individual was then asked to hold the head steady, and when lifting the arm, to look at the

bar, and try to keep pace with the metronome. With the beat, they should begin to raise the

arm to the bar, and on the next beat, they should lower the arm to the switch contact with a

smooth motion. The examiner, a manual therapist experienced in ultrasound recordings of the

neck, held the probe. The other physiotherapist showed the participants how to perform the

test and assisted the ultrasound examiner; for example, at the request of the examiner, the

assistant might save the ultrasound imaging sequence in the ultrasound database. Thus, the

physiotherapist holding the probe could concentrate on holding the probe in a stable position

to capture clear images of the muscles of interest throughout the entire test.

Fig. 2. An ultrasound image showing superficial and deep ventral neck muscles. Three

regions of interest (ROIs; each indicated as a blue line with a square on each end) were

A

C

B

selected in each muscle for post-process speckle tracking analysis. A = Sternocleidomastoid,

B = Longus capitis, C = Longus colli.

Fig. 3. Different muscle deformation sequences that can occur during one arm elevation.

This diagram illustrates three different patterns of muscle deformations obtained for three

different individuals (each line represents deformations in one individual). Each line

represents the changes observed in the ROI (deformation %) in one muscle, during one arm

elevation. The region (area) below zero (negative values) represents muscle shortening and

the region (area) above zero (positive values) represents muscle elongation. The total area

(sum of negative and positive areas) represents the total muscle deformation during one arm

elevation. When the line crosses the 0% line, the muscle switches from shortening to

elongation, or vice versa.

a) b)

c) d)

e) f)

Fig. 4 a-f. Relationships between total deformation areas of muscle pairs. Linear

relationships between muscle pairs are shown for the first and tenth arm elevations.

(a,b) Relationships between sternocleidomastoid (SCM) and longus colli (Lco) muscles: (Top

panels) Controls showed amoderate linear relationship during the 10th (R2= 0.53) arm elevations

compared to the first (weak; R2 = 0.25); (bottom panels) individuals with WAD showed no linear

relationships (R2< 0.02).

(c,d) Relationships between SCM and longus capitis (Lcap) muscles: (Top panels) Controls

showed higher linear relationships (moderate) during the 10th (R2= 0.43) arm elevations

compared to the first (R2 = 0.35); (bottom panels) individuals with WAD showed no linear

relationships (R2= 0.08 to 0.03).

(e,f) Relationships between Lcap and Lco: Both groups showed moderate linear relationships

during the 10th arm elevations compared to the weak linear relationship at the first arm

elevations; (top panels) controls (R2 = 0.14 to 0.51); (bottom panels) individuals with WAD

(R2= 0.13 to 0.57).

a) b)

c) d)

e) f)

Fig. 5 a-f. Relationships between deformation rates of muscle pairs. Linear relationships

between muscle pairs are shown for the first and tenth arm elevations.

(a,b) Relationships between sternocleidomastoid (SCM) and longus colli (Lco) muscles: (Top

panels) Controls showed a strong linear relationship during both the 1st and the 10th arm

elevations (R2= 0.70); (bottom panels) individuals with WAD showed a weak linear relationships

during the tenth arm elevations (R2= 0.14) compared to the first (moderate; R2= 0.30).

(c,d) Relationships between SCM and Longus capitis (Lcap) muscles: (Top panels) Controls

showed a strong linear relationship during the 10th arm elevations (R2= 0.71) compared to the

first (moderate; R2 = 0.43); (bottom panels) individuals with WAD showed a weak linear

relationship during the 10th arm elevations (R2 = 0.07) compared to the first (moderate; R2 =

0.44).

(e,f) Relationships between Lcap and Lco muscles: (Top panels) controls showed equivalent

linear relationships during the 1st and 10th arm elevations (moderate; R2= 0.53); (bottom panels)

individuals with WAD showed a weak linear relationship during the 10th arm elevations (R2 =

0.19) compared to the first (moderate; R2 = 0.43).